The elevator is a device which transmits people or goods vertically against gravity, which is used in many buildings. Generally, the elevators may be divided into rope-type elevators and hydrodynamic elevators according to their driving mechanism, or may be divided into screw-type and rack-n-pinion-type. In these days, elevators using a linear motor instead of an elevator traction machine have appeared.
The rope-type elevator comprises a machine room for driving the elevator at the highest floor, the traction machine of which connects a car and a balance weight via a rope to move the car vertically. The machine room for the traction machine has a several limitations, such as its height and weight, to adversely affect the building design.
As the number of the skyscrapers increases, high-speed elevators which can move at speeds over 60 km/h (1000 m/min) have been actively developed. Moreover, newly developed are double-deck elevators which transmit two cars at once and twin elevators which transmit two cars independently.
The high-rise buildings need a high-speed elevator in order to effective vertical transportation. To increase the velocity of the rope-type elevator, its rope must endure a tension proportional to the square of the velocity. Accordingly, as increasing the speed of the elevator, its ropes or wires should have a thicker cross-section and a heavier weight. Moreover, since the length of the ropes should be as long as the height of the high-rise building, the ropes should be much thicker because of the weight of itself, if not by the elevator velocity. In the end, the ropes of the elevator might be heavier than the car in the high-rise buildings or skyscraper.
For reference, the elevators may be divided into low-speed elevators which move at speed of below 45 m/min, mid-speed elevators which move at speed of about 60˜105 m/min, high-speed elevators which move at speed of 120˜300 m/min, and ultrahigh-speed elevators which move at speed of over 360 m/min.
Actually, one of the ultrahigh-speed elevators of “Burj Dubai” building is known to have about 20 tons of ropes. Considering the chains and the balance weights, the ultrahigh-speed elevator must need much larger power to increase its speed. Thus, the traction machine of the high-speed elevator in the high-rise buildings should be more powerful and bigger than those of other normal elevators.
The longer the elevator rope is, the more difficult the control of the elevator stop position is, due to the rope's inertia, the rope's elasticity dependent on temperature and the like. So, the elongation of the elevator rope makes elevator control more difficult and complicated.
On the other hand, there is a screw-type elevator which uses a long pole with male screw and a sleeve with female screw attached on the elevator car. The screw-type elevator transports the car by rotating the long pole, so as to be applied as a simple or small-size elevator.
However, it is expected that ropeless elevators may be used into over 100 stories of buildings instead of the conventional rope-type elevators. U.S. Pat. No. 5,234,079 discloses a elevator applying a linear motor. Since this linear elevator moves in hanging in the air without rope, the elevator might be rather dangerous and needs double or triple safety lock devices.